MADRID (Reuters) - Spain's conservative acting prime minister, Mariano Rajoy, will call the heads of the Socialist Party and the liberal Ciudadanos on Friday, to seek their support to form a government.

Spain has been without a proper government since an inconclusive election in December. Rajoy's People's Party won more parliamentary seats at a second vote in June, but did not reach the 176 needed to form a majority government.

A party spokesman told TVE television Rajoy would call Socialist leader Pedro Sanchez and Albert Rivera, head of the fourth-placed Ciudadanos, and was eager "to form a government as soon as possible."

He needs the support or at least the abstention of both to win a confidence vote in the 350-seat lower house of parliament.

Despite the political uncertainty, Spain has continued to rebound from a punishing recession that started with a real-estate crisis in 2008.

The government raised its economic growth forecast for 2016 on Friday to 2.9 percent from 2.7 percent previously, as it prepares next year's budget, which could be delayed if Spain remains without a government beyond September.

Rajoy has not said when he might call the confidence vote but said he hoped Spain would have a government and pass its budget in time for a European Union deadline in October.